The present invention relates to an improved adhesive suitable for use in ink jet printers, and more particularly, to a flexible adhesive for attaching ink jet printheads to print cartridge containers.
In the production of thermal ink jet print cartridges for use in ink jet printers, a printhead is bonded to a print cartridge container. The printhead includes an ink-receiving opening and ink supply channels through which ink travels to a plurality of bubble chambers. Each bubble chamber includes a resistor which, when addressed with an energy pulse, momentarily vaporizes the ink and forms a bubble which expels an ink droplet. The printhead typically comprises a heater chip and a nozzle plate having a plurality of discharge orifices formed therein.
The container serves as a reservoir for the ink and includes a fluid supply opening which communicates with the ink-receiving opening of the printhead for supplying ink to the bubble chambers in the printhead.
During assembly of the printhead to the print cartridge container, an adhesive is used to bond the two elements together. The flexible adhesive also xe2x80x9cfixesxe2x80x9d the printhead to the print cartridge container such that its location relative to the print cartridge container is known and does not shift during processing or use. Further, the flexible adhesive provides an additional function in serving as a fluid gasket against leakage of ink.
However, the printhead and the print cartridge container typically have dissimilar coefficients of thermal expansion, since the surface of the printhead bonded to the print cartridge container most commonly is silicon and the print cartridge container is, for example, a polymeric material such as a modified phenylene oxide. Thus, the flexible adhesive must accommodate both the dissimilar expansions and contractions of the printhead and the print cartridge container and be impermeable to attack by the ink, which is commonly in a vehicle of water and at least one glycol and/or glycol ether plus a colorant, plus substances such as pH modifiers, biocides, etc.
Typical adhesive materials comprise an epoxy resin, such as a bisphenol-A based epoxy resin, a cross-linking agent and an initiator. They may also include pigments and modifiers to alter their physical properties. Some conventional adhesives offer good adhesive properties and others offer good chemical resistance to inks. However, none of these conventional adhesives exhibit good adhesion properties while at the same time exhibiting good chemical resistance to inks.
Additionally, conventional adhesive materials often comprise anhydride cross-linkers which typically absorb water and result in voids (air pockets) in the flexible adhesive upon curing. Such voids are not desirable because they can, for example, result in a non-homogeneous adhesive having poor adhesion characteristics. They may also cause mixing of inks as a result of channel formation in the adhesive layer. Further, adhesive materials comprising anhydrides typically have poor shelf lives and poor pot lives, and, therefore, are often difficult to work with and store.
Conventional adhesive materials also tend to be non-flexible and brittle after curing. This causes the adhesive materials to often chip or crack. It also can cause the components (e.g., printhead and ink jet print cartridge container) that the adhesive material is keeping together to come apart, chip or crack. Such events can result in ink leakage and poor adhesion as well as malfunctioning of ink jet printers. Moreover, attempts to make adhesive materials more flexible after curing often lead to adhesive materials that are not resistant to chemical degradation by inks.
Accordingly, it is seen that a need exists in the art for a flexible adhesive composition suitable for use in ink jet printers, and particularly, for attaching printheads to print cartridge containers.
This need is met by the present invention, wherein adhesive compositions are provided which exhibit superior adhesion properties while at the same time unexpectedly exhibiting good chemical resistance to inks as well as acceptable pot lives and shelf lives. Moreover, the adhesive compositions of this invention unexpectedly are substantially depleted of voids after curing and are flexible and non-brittle after curing.
In a first embodiment, the present invention is directed to a flexible adhesive composition comprising: (a) an additive comprising at least one multifunctional compound selected from the group consisting of a monomer, oligomer and polymer; (b) at least one non-acrylic silane coupling agent selected from the group consisting of a non-acrylic silane coupling agent capable of becoming an electrophile and a non-acrylic silane coupling agent capable of becoming a nucleophile; and (c) a flexibility modifier, with the proviso that the flexible adhesive composition does not comprise an anhydride.
In a second embodiment, the present invention is directed to an ink jet print cartridge container comprising the novel flexible adhesive compositions of this invention to bond a printhead thereto.
In a third embodiment, the present invention is directed to a method for attaching a printhead to an ink jet print cartridge container.
While the flexible adhesive compositions of this invention comprise the constituents mentioned above (e.g., the additive, coupling agent and flexibility modifier), it is within the scope of this invention for the flexible adhesive composition to consist essentially of or consist of the same.